Means for insulating elements of a low temperature unit



c. TREPP 3,092,283

MEANS FOR INSULATING ELEMENTS OF' A LOW TEMPERATURE UNIT June 4, 1963Filed July 20, 1961 United States Patent @ffice 3,092,283 Patented June4, 1963 3,092,283 MEANS FOR INSULATING ELEMENTS F A LOW TEMPERATURE UNTChristian Trepp, Zurich, Switzerland, assignor to Sulzer Freres, SA.,Winterthur, Switzerland, a corporation of Switzerland Filed July 20,1961, Ser. No. 125,440 Claims priority, application Switzerland July 29,1960 6 Claims. (Cl. 2210-16) The present invention relates to means forimproving the insulation of elements of low temperature apparatus suchas that which is employed for example in the liquefaction of diflicultlyliqueiiable gases such as hydrogen or helium.

The practice of protecting elements of devices which operate at lowtemperatures from absorbing external heat is quite common. 'Ihis isparticularly true of those elements where an appreciable temperaturedilerential is maintained such as heat exchangers, rectifying columnsand the like. One manner in which this may be accomplished is to placethe elements in a vacuum jacket or vessel and then to further insulatethem by employing a timely-divided insulating material to fill the openspace in the vacuum jacket and to surround the elements being insulated.In order to inspect elements which are insulated in this way it is thennecessary to remove the insulating material completely from the jacket.In addition, the elective operation of these low temperature units issomewhat hindered and eiective operation is delayed after start upbecause of the presence of appreciable quantities of the insulatingmaterial in the vacuum jacket since the heat content of this materialmust be removed before the elements can function at optimum capacity.

It is, therefore, an important object of this invention to provideimproved insulating means adapted for use as additional insulation forelements which are normally operated at low temperature and within anevacuated vessel maintained at subatrnospheric pressure.

Another object of this invention is to provide such auxiliary insulatingmeans which may be readily applied to and removed from said elements foreasy inspection and access.

Other objects of this invention will appear from the following detaileddescription and the accompanying drawing.

It has now been found that the disadvantages of the insulating methodsand materials heretofore employed in the insulation of low temperatureelements may be overcome and highly ecient insulation achieved ifseveral elements of a low temperature device are each enclosed within ashaped jacket formed of a rigid porous insulating material and theenclosed elements are then maintained and operated in a vacuum vesselheld at a pressure of 10-1 to 10-3 millimeters of mercury.

As the rigid porous insulation material used in forming the shapedjacket there may be employed :any one or more of those materials whichare generally employed as protective agents for refrigeration equipmentsuch as, for example, naturally occurring organic material such as corkparticles, granular plastic materials or inorganic substances, sheets or'batts of foamed synthetic plastic resin materials or sheets or battsformed of brous materials such as mineral wool. In accordance with thepresent invention the required degree of insulation can be readilyattained by maintaining a vacuum of from l0-1 to iiD-3 millimeters ofmercury in the vessel containing the insulated elements since theinsulating material contains pores whose dimensions are less than themaximum distance of the mean free path of the gaseous molecules of theair at the indicated pressures.

Advantageously, the jacket or casing which serves as the insulationmaterial is so assembled and mounted as to `be removable at least inpart so that when inspection is required the insulated elements arereadily accessible. By employing a concentric arrangement powdered,granular or iibrous materials such as easily pourable kieselguhr oreasily laminated asbestos, spun glass bers or rock wool may be utilizedand in each case the outer protective shell is advantageously formed ofa screen-like material which is provided with a suitable removablebonnet or header. lf the insulating casing is formed of sheet materialssuch as oamed plastic, this is likewise mounted on the equipment so asto be easily removable. For example, by means of catches at the marginof the sheet or by the use of wire strapping or with clasps theinsulating sheet material can be brought into very close contact withthe equipment. The protective casing cau also be so designed that noparticular fastening agents `are required.

In order to reduce heat absorption due to radiation a metal powder mayconveniently be incorporated into the outer layer of the casing to deectradiant heat and, similarly, a metal foil may be applied to the outersurface of the casing or jacket for the same purpose.

Other `features of the invention will be apparent upon reference to thedescription and the accompanying drawing which comprises a `schematicdiagram Iwhich illustrates one method whereby the invention may becarried out.

Referring to the drawing, the reference numeral 1 iudicates a vacuumtank provided with a removable cap 2. Connected to the tank 1 is a pipe3 which is further connected to sa pump, not shown, such as a rotarypump, capable of producing and maintaining a vacuum of 10 1 to 10-3 mm.of mercury within the tank. The tank 1, as shown, contains a heatexchanger 4 and a rectifying column 5 which are supported by but areinsulated from the walls of said tank by suitable brackets. Therectifying column 5 is enclosed within a jacket or casing 6 formed of agranular insulating material. 'Ihe outer layer of the casing is formedof a screen-like or foraminous sheath 7 which may be, for example, aperforated metal foil. The foraminous sheath may be formed in sections,the upper portion consisting of a removable bonnet or header, asdescribed above, which may be attached to the lower portion by means ofsuitable anges in the manner shown in the drawing, similar to the mannerin which removable cap 2 is attached to the lower portion of tank 1. Anopening for introducing lthe powdered, granular or fibrous insulatingmaterial into sheath 7 and having :a removable closure may be providedin the top of the removable bonnet or header. Surrounding the heatexchanger 4, as shown, is a sheet material formed of a foamed plastic-material 8 which is held in position in close proximity to the outersurface of said heat exchanger by means of clamps 9 and 10, or by otherfastening means. As shown, sheet material S is slit beneath clamps 9 and10 respectively so that by opening said clamps the top and bottom capsformed by said slits can be removed.

I claim:

1. In an apparatus having a plurality of elements operating at lowtemperatures, an outer casing for each of said elements, said casingsbeing formed of porous heat insulating material, and a vessel maintainedat a vacuum of from 10-1 to 10-3 mm. of mercury containing saidelements.

2. In an apparatus in accordance with claim l and wherein the outersurface of said outer casings contains a metal powder yas 'a shieldagainst absorption of heat radiation.

3. In an apparatus in accordance with claim l and wherein the outersurface of said outer casings is provided with Ia metal foil as a shieldagainst absorption References Cited in the file of this patent of heatradiation. NIT

4. In an apparatus in accordance with claim 1 and U ED STATES PATENTS 5.In an apparatus in accordance with claim 1 and 2,962,867 Seidel Dec. 6,1960 'wherein said outer casings are formed by Yremovably 2,970,452Beckman et al. Feb. 7, 1961 mmd Sheetmaals: s OTHER REFERENCES In anapparatus 1n accordance w1th clalm 1 and l wherein the heat insulatingmaterial employed is a granu- 10 Progress In CfY0gDlCS(lVIeIldelSSOhll),` Published Ylar material; and a screen-like sheath isprovided surround- 'by Academic Press, Incorporated (New York), 1960,ing the granular material. (pages 78-85 relied on).

1. IN AN APPARATUS HAVING A PLURALITY OF ELEMENTS OPERATING AT LOWTEMPERATURES, AN OUTER CASING FOR EACH OF SAID ELEMENTS, SAID CASINGSBEING FORMED OF POROUS HEAT INSULATING MATERIAL, AND A VESSEL MAINTAINEDAT A VACUUM OF FROM 10-1 TO 10-3 MM. OF MERCURY CONTAINING SAIDELEMENTS.